Optical device unit and detection apparatus

ABSTRACT

An optical device unit includes: an optical device which has an electrical conductor and is capable of enhancing Raman scattering light generated by receiving light from a light source; and a first guide unit which guides a gaseous sample to the optical device. The optical device unit is detachable from the detection apparatus.

BACKGROUND

1. Technical Field

The present invention relates to an optical device unit and a detectionapparatus.

2. Related Art

In general, a Raman spectroscopic apparatus includes a detector forobtaining Raman spectra by detecting Raman scattering light depending ona detection target substance. The detection target substance can bespecified by performing a spectroscopic analysis using the Ramanspectra. However, the signal intensity of the Raman scattering light istypically weak, and its detection sensitivity is low.

JP-T-2008-529006 discloses a handheld Raman blood analyzer to providesurface-enhanced Raman scattering using gold colloid sol-gel/strips andincrease the signal intensity of the Raman scattering light.

In addition, a localized plasmon can be generated by irradiatingexcitation light onto a metal surface. The electric field can be locallyenhanced by combining the excitation light and the localized plasmon. Itis envisaged that Raman scattering light is enhanced by the enhancedelectric field in the surface-enhanced Raman scattering.

Japanese Patent No. 3482824 discloses a vertical cavity surface-emittinglaser (VCSEL) capable of safely controlling a polarization surface inwhich excitation light can be provided using the VCSEL.

Optical absorption is generated by localized plasmon resonance whenexcitation light and localized plasmon are combined. For example,JP-A-2000-356587 discloses a technique of improving sensor sensitivitybased on localized surface plasmon resonance using a substrate having asurface where metal micro particles are fixed. JP-A-2007-10648 disclosesa localized plasmon resonance sensor having a resonance peak shifted toa long wavelength side and a resonance peak shifted to a shortwavelength side. In addition, JP-A-2009-250951 discloses an electricfield enhancement device including a micro resonator having a pluralityof resonance areas in order to make it possible to resonate for aplurality of wavelengths.

A Raman spectroscopic apparatus typically includes an optical devicehaving an electrical conductor such as a metal nano-structure where adetection target substance can be adsorbed. Raman scattering lightcaused by an enhanced electric field can be detected by guiding thetarget substance into the enhanced electrical field near the opticaldevice. Depending on the type of target substance, or the type ofoptical device, a detection sensitivity of the Raman scattering lightmay be low.

SUMMARY

An advantage of some aspects of the invention is to provide an opticaldevice unit and a detection apparatus capable of improving the detectionsensitivity.

An aspect of the invention is directed to a detachable optical deviceunit to a detection apparatus, the optical device unit including: anoptical device having an electrical conductor, the optical device beingcapable of enhancing Raman scattering light generated by receiving lightfrom a light source of the detection apparatus; and a first guide unitthat guides a gaseous sample to the optical device.

In the optical device unit of the aspect of the invention, the usedoptical device unit may be removed from the detection apparatus, and anew optical device unit may be installed in the detection apparatus. Ifthe optical device unit is exchanged in this manner, it is possible toincrease detection sensitivity of the detection apparatus while thegaseous samples attached to the first guide unit and the optical devicedo not influence the subsequent detection or measurement.

In the optical device unit of the aspect of the invention, the firstguide unit may have a first fluid path that imports the gaseous samplefrom an import hole, and the first fluid path may have an inner wallsurface that blocks an incident ray of external light between the importhole and the optical device.

As a result, external light rarely reaches the optical device, and aratio of the external light (noise) with respect to the Raman scatteringlight (signal) decreases. Therefore, it is possible to improve asignal-to-noise ratio (S/N ratio) when the Raman scattering light isdetected and increase the detection sensitivity.

The optical device unit of the aspect of the invention may furtherinclude a filter for removing dust in the air in the first fluid path,and the filter may block the external light.

As a result, dust and external light rarely arrive at the optical devicedue to the presence of the filter, and it is possible to increase thedetection sensitivity.

The optical device unit of the aspect of the invention may furtherinclude an identification code that can be read by the detectionapparatus and identifies the optical device.

As a result, the detection apparatus can recognize the type of theoptical device or the gaseous sample detectable by the optical device.In a case where the detection apparatus carries out a spectroscopicanalysis using Raman spectra, such a detection apparatus (Ramanspectroscopic apparatus) can easily detect or specify the gaseous sample(target substance) corresponding to the optical device.

In the optical device unit of the aspect of the invention, the firstguide unit may have a second fluid path connected to the first fluidpath, and the second fluid path may rotate the gaseous sample in an areafacing the optical device.

As a result, due to presence of the second fluid path of the guide unit,a possibility that the gaseous sample enters the optical deviceincreases. Therefore, the signal intensity of the Raman scattering lightbecomes stable. For example, even when the amount of the gaseous sampleis small, it is possible to easily detect or specify the gaseous sample(a target substance).

Another aspect of the invention is directed to a detection apparatusincluding: the optical device unit described above, a second guide unitconnectable to the first guide unit; the light source; a first opticalsystem that introduces the light from the light source into theelectrical conductor of the optical device; and a detector that detectsRaman scattering light from the light scattered or reflected by theelectrical conductor, wherein the second guide unit guides the gaseoussample to the outlet duct.

As a result, by connecting the first guide unit of the optical deviceunit and the second guide unit of the detection apparatus, it ispossible to provide a detection apparatus in which the optical deviceunit is exchangeable.

In the detection apparatus of the aspect of the invention, theelectrical conductor of the optical device may include a firstprotrusion group having a plurality of protrusions, each of theplurality of protrusions of the first protrusion group may be arrangedwith a first period along a direction parallel to the virtual plane ofthe electrical conductor, and the first optical system introduces thelight from the light source into the first protrusion group such that acomponent parallel to the virtual plane of a polarization direction ofthe light from the light source is parallel to an arrangement directionof the first protrusion group.

As a result, the enhanced electric field of the optical device can beincreased by the first protrusion group. In addition, linearly-polarizedlight in which a component parallel to the virtual plane of thepolarization direction is parallel to the arrangement direction of thefirst protrusion group can be incident to the optical device. As aresult, propagation type surface plasmons can be excited.

In the detection apparatus of the aspect of the invention, each of theplurality of the protrusions of the first protrusion group may include asecond protrusion group formed of an electrical conductor on a frontsurface of the first protrusion group, and each of a plurality ofprotrusions of the second protrusion group corresponding to any one ofthe plurality of protrusions of the first protrusion group may bearranged with a second period shorter than the first period along adirection parallel to the virtual plane.

As a result, the enhanced electric field in the optical device canincrease also in the second protrusion group.

The detection apparatus of the aspect of the invention may furtherinclude a third protrusion group formed of a third electrical conductoron a surface between neighboring protrusions of the first protrusiongroup on a surface where the first protrusion group is arranged, andeach of a plurality of protrusions of the third protrusion group may bearranged with a third period shorter than the first period along thedirection parallel to the virtual plane between the neighboringprotrusions of the first protrusion group.

As a result, the enhanced electric field in the optical device canincrease also in the third protrusion group.

In the detection apparatus of the aspect of the invention, surfaceplasmon resonance in the event that a propagating direction of the lightfrom the light source is inclined with respect to a normal line directedto the virtual plane may be generated in each of first and secondresonance peak wavelengths, a first resonance peak wavelength bandhaving the first resonance peak wavelength may have an excitationwavelength in surface-enhanced Raman scattering caused by the surfaceplasmon resonance, and a second resonance peak wavelength band havingthe second resonance peak wavelength may have a Raman scatteringwavelength in the surface-enhanced Raman scattering.

As a result, surface plasmon resonance is generated in each of the firstand second resonance peak wavelengths by the light incident to the firstprotrusion group in which protrusions are arranged with the firstperiod. In this case, the incident angle of the light and the firstperiod are set such that the first resonance peak wavelength bandincluding the first resonance peak wavelength includes an excitationwavelength of surface-enhanced Raman scattering, and the secondresonance peak wavelength band of the second resonance peak wavelengthincludes a Raman scattering wavelength in surface-enhanced Ramanscattering. As a result, it is possible to improve an enhancement degreeof the electric field in both the excitation wavelength and the Ramanscattering wavelength.

The detection apparatus of the aspect of the invention may furtherinclude a second optical system that guides the Raman scattering lightto the detector, and the detector may receive the Raman scattering lightthrough the second optical system.

As a result, it is possible to efficiently receive the Raman scatteringlight using the second optical system.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described with reference to the accompanyingdrawings, wherein like numbers reference like elements.

FIGS. 1A to 1D illustrate a configuration example of a detectionapparatus including an optical device unit according to an embodiment ofthe invention.

FIGS. 2A to 2E are explanatory diagrams of the principle of detectingRaman scattering light.

FIGS. 3A to 3D illustrate a specific configuration example of adetection apparatus including an optical device unit according to anembodiment of the invention.

FIG. 4 is an exemplary block diagram illustrating the detectionapparatus of FIG. 3A.

FIGS. 5A and 5B illustrate an exemplary structure of a vertical cavitysurface-emitting laser (VCSEL).

FIG. 6 is an explanatory diagram illustrating characteristics of lightsources.

FIGS. 7A to 7C illustrate exemplary configurations of a guide unit and adischarge fluid path.

FIGS. 8A to 8E are schematic explanatory diagrams illustrating aphotolithographic technique.

FIGS. 9A to 9E are schematic explanatory diagrams illustrating amanufacturing process of a metal nano-structure.

FIGS. 10A to 10C are schematic explanatory diagrams illustrating anenhanced electric field formed in a metal nano-structure.

FIG. 11 is a schematic explanatory diagram illustrating two resonancepeaks.

FIG. 12 is a perspective view illustrating a configuration example of asensor chip.

FIG. 13 is a cross-sectional view illustrating the sensor chip of FIG.12.

FIG. 14 illustrates an exemplary characteristic of a reflective lightintensity of a sensor chip.

FIG. 15 is an explanatory diagram illustrating an excitation conditionof surface plasmon polaritons.

FIG. 16 illustrates another exemplary characteristic of a reflectivelight intensity of a sensor chip.

FIG. 17 is a perspective view illustrating a modified example of thesensor chip of FIG. 12.

FIG. 18 is a cross-sectional view illustrating the sensor chip of FIG.17.

FIGS. 19A and 19B are explanatory diagrams illustrating a technique forintroducing incident light into a sensor chip with an inclination.

FIGS. 20A and 20B are schematic explanatory diagrams illustrating amethod of manufacturing an electrical conductor.

FIGS. 21A to 21C are schematic explanatory diagrams illustrating peakextraction from Raman spectra.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

Hereinafter, preferable embodiments of the invention will be describedin detail. Embodiments of the invention described below are not intendedto limit the scope of the invention described in the claims, and all ofthe configurations described in the embodiments of the invention are notnecessarily indispensable as solving means of the invention.

1. Overview

1.1. Basic Configuration

FIGS. 1A to 1D illustrate an exemplary configuration of a detectionapparatus including an optical device unit according to an embodiment ofthe invention. As shown in FIG. 1A, the optical device unit includes anoptical device 4 and a guide unit 420 (first guide unit), and thedetection apparatus includes the optical device unit, a discharge fluidpath 423 (second guide unit), a light source A, an optical system, and adetector 5. The optical device unit is detachable from the detectionapparatus, and the guide unit 420 and the discharge fluid path 423 areconnected thereto.

The optical system (first optical system) includes a half mirror 2 andan object lens 3. The light source A may radiate light having apredetermined polarization direction. In addition, the light source A isnot limited to the example in FIG. 1A but may include a plurality oflight sources. In addition, the light source A may have directivity.Preferably, the light source A may have a light source with highdirectivity (for example, laser).

The half mirror 2 and the object lens 3 (in the broadest sense, theoptical system) introduces the light from the light source A into theelectrical conductor of the optical device 4. In addition, the guideunit 420 guides the gaseous sample to the optical device 4. Thedischarge fluid path 423 is guided to the optical device 4 anddischarges the gaseous sample. The detector 5 detects the Ramanscattering light from the light scattered or reflected by the electricalconductor. The detection apparatus may be called a Raman detectionapparatus, and the detection apparatus further performing aspectroscopic analysis using Raman spectra may also be called a Ramanspectroscopic apparatus.

The inventors have recognized that the gaseous sample is continuouslyattached to the optical device 4 and the guide unit 420 used in theRaman spectroscopic apparatus, and the signal intensity of the Ramanscattering light caused by the enhanced electric field in the vicinityof the electrical conductor of the optical device 4 is not stable. Inthis regard, it is possible to increase the detection sensitivity of thedetector 5 by separating the optical device 4 and the guide unit 420 andby improving the guide unit 420 in some cases. In addition, it ispossible to improve the detection sensitivity by separating the opticaldevice 4 and the guide unit 420 from the detection apparatus. Inaddition, it is possible to increase a possibility that the gaseoussample enters the optical device by improving the guide unit 420.Therefore, it is possible to obtain a stable signal intensity of theRaman scattering light. The Raman scattering light and the enhancedelectric field will be described below. In addition, the guide unit 420will be described below.

In the example in FIG. 1A, the optical path of the light Lin (incidentlight) from the light source A and the optical path of the light Lout(scattered light, reflective light) from the optical device 4 do notaccurately represent the actual optical path. In other words, they areintended to only show presence of the optical path of the light Lin(incident light) from the light source A and presence of the opticalpath of the light Lout (scattered light, reflective light) from theoptical device 4.

In the example in FIG. 1B, the detection apparatus may include a controlunit 7 that variably controls the relative position between the opticaldevice 4 and the light source A. Specifically, the control unit 7 maychange the position of the light source A. In addition, the control unit7 may include an operation unit such as an XY stage or may only transmita signal to the operational unit.

The control unit 7 may change the position of the optical device 4. Inthe example in FIG. 1B, the control unit 7 changes the position of thelight source A such that the optical axis Lax1 of the light source Amatches the optical axis Lax2 of the object lens 3 (in the broadestsense, the optical axis of the optical system).

In this case, in practice, it is anticipated that the light Lin from thelight source A is overlapped with the optical axis Lax1 of the lightsource A and the optical axis Lax2 of the object lens 3. However, in theexample in FIG. 1B, the light Lin from the light source A is illustratedso as not to be overlapped with the optical axis Lax1 of the lightsource A and the optical axis Lax2 of the object lens 3. In the examplein FIG. 1B, in order to illustrate that the optical axis Lax1 of thelight source A matches the optical axis Lax2 of the object lens 3, thelight Lin from the light source A is illustrated so as not to beoverlapped with the optical axis Lax1 of the light source A and theoptical axis Lax2 of the object lens 3.

In the example in FIG. 1C, the control unit 7 changes the position ofthe light source A such that the optical axis Lax1 of the light source Ais deviated from the optical axis Lax2 of the object lens 3. In thiscase, in practice, it is anticipated that the light Lin from the lightsource A is overlapped with the optical axis Lax1 of the light source A.However, in the example in FIG. 1C, the light Lin from the light sourceA is illustrated so as not to be overlapped with the optical axis Lax1of the light source A. In the example in FIG. 1C, in order to illustratethat the optical axis Lax1 of the light source A does not match theoptical axis Lax2 of the object lens 3, the light Lin from the lightsource A is illustrated so as not to be overlapped with the optical axisLax1 of the light source A.

In the example in FIG. 1D, the detection apparatus may have a controlunit 7 for variably controlling a relative position between the opticaldevice 4 and the optical system. Specifically, the control unit 7 maychange a position of the object lens 3. It is possible to match theoptical axis of the light source A with the optical axis of the objectlens 3 by changing the position of the object lens 3. Otherwise, theoptical axis of the light source A may be deviated from the optical axisof the object lens.

1.2. Principle of Detection

FIGS. 2A to 2E are explanatory diagrams illustrating the principle ofdetection in the Raman scattering light. The example in FIG. 2Aillustrates Raman spectroscopy, in which, when the incident light(frequency ν) is irradiated onto a target molecule (in the broadestsense, a target substance), a significant amount of the incident lightis scattered as Rayleigh scattering light, and a frequency ν or awavelength of the Rayleigh scattering light is not changed. A part ofthe incident light is scattered as Raman scattering light, and thefrequency (ν−ν′ and ν+ν′) or the wavelength of the Raman scatteringlight is reflected on the frequency ν′ (molecular vibration) of thetarget molecule. A part of the incident light is used to vibrate thetarget molecule to reduce energy. However, the vibration energy of thetarget molecule may be added to optical energy or vibration energy ofthe Raman scattering light. Such a shift (ν′) of the frequency is calleda Raman shift.

The example in FIG. 2B illustrates a Raman spectrum in a case where thetarget molecule is a molecule of acetaldehyde. In other words, it ispossible to specify a molecule of acetaldehyde by analyzing the Ramanspectrum shown in FIG. 2B. However, in a case where the amount of targetmolecules is small, the Raman scattering light is typically too weak todetect or specify the target molecule. In this regard, it is preferablethat the Raman scattering light be enhanced by the enhanced electricfield by adding the enhanced electric field. In addition, the Ramanspectrum in FIG. 2B shows the Raman shift using the wave number.

The example in FIG. 2C illustrates an enhanced electric field formedwhen the incident light (irradiated light) is irradiated onto the metalfine-particle 20. In a case where the incident light is irradiated ontometal fine-particles 20 (metal nano-particles) smaller than thewavelength of the incident light, the electric field of the incidentlight is applied to free electrons present on the surfaces of the metalfine-particles 20 to generate resonance. As a result, the electricdipole caused by the free electrons is excited within the metalfine-particles 20 so that an enhanced electric field stronger than theelectric field of the incident light is formed in the vicinity of themetal fine-particles 20. Such a phenomenon is unique in electricconductors such as metal fine-particles 20 smaller than the wavelengthof the incident light.

The example in FIG. 2D illustrates surface-enhanced Raman scattering(SERS) when the incident light is irradiated onto the optical device 4.The optical device 4 includes a substrate 100. It is possible to providea protrusion group 115 (in the broadest sense, a metal nano-structure)having a plurality of protrusions 110 by forming metal fine-particles 20in convex portions 105 of the substrate 100. It is possible to form anenhanced electric field between neighboring protrusions 110 (electricalconductors formed in the convex portions 105) of the protrusion group115 by irradiating incident light onto such an optical device. If thetarget molecule enters the enhanced electric field, the Raman scatteringlight caused by the target molecule is enhanced by the enhanced electricfield, and the signal intensity of the Raman scattering light becomesstrong. In such surface-enhanced Raman scattering, it is possible toincrease detection sensitivity even when the number of target moleculesis insignificant.

Although the incident light is irradiated from the surface side (theelectrical conductor side) of the optical device 4 in the example inFIG. 2D, the incident light may be irradiated from the rear side (thesubstrate 100 side) of the optical device 4 as shown in FIG. 2E. In theexample in FIG. 2E, it is possible to detect the Raman scattering lightand the Rayleigh scattering light on the rear side of the optical device4.

The optical device 4 illustrated in FIGS. 1A to 1D preferably has ametal nano-structure as shown in FIG. 2D. However, it may not benecessary to provide the enhanced electric field as shown in FIG. 2C.

2. Specific Example

2.1. Entire Configuration

FIGS. 3A to 3D illustrate an exemplary configuration of the detectionapparatus having the optical device unit in detail according to anembodiment of the invention. In the following description, likereference numerals denote like elements as in FIG. 1, and descriptionthereof will not be repeated. In the example in FIG. 3A, the opticaldevice unit is integrated in the detection apparatus. In the example inFIG. 3B, the optical device unit is extracted from the detectionapparatus before the optical device unit is integrated. In the examplein FIG. 3C, the optical device unit for exchange is illustrated. In theexample in FIG. 3D, an entrance path of the external light isillustrated. In order to increase the detection sensitivity of thedetection apparatus, the optical device unit is detachably integrated inthe detection apparatus. By removing the used optical device unit fromthe detection apparatus and installing a new optical device unit in thedetection apparatus, the gaseous sample attached to the guide unit 420and the optical device 4 does not affect the subsequent detection ormeasurement.

The optical device unit of the detection apparatus in FIG. 3A includes asensor chip 300 (in the broadest sense, the optical device 4) and aguide unit 420 (transport unit). The target substance is introduced fromthe inlet duct 400 (loading entrance or import hole) to the inner sideof the guide unit 420 (first guide unit) and the discharge fluid path423 (second guide unit) and discharged from the outlet duct 410 to theouter side of the guide unit 420 (first guide unit) and the dischargefluid path 423 (second guide unit). In the example in FIG. 3A, thedetection apparatus includes a fan 450 (in the broadest sense, suctionunit) near the outlet duct 410 so that pressures within the inlet fluidpath 421 (first fluid path) of the guide unit 420, the fluid path 422(second fluid path) in an area facing the sensor chip 300, and thedischarge fluid path 423 (third fluid path) are reduced as the fan 450is operated. As a result, the target substance (gaseous sample) isimported to the guide portion 420. The target substance passes throughthe fluid path 422 near the sensor chip 300 via the inlet fluid path 421and is discharged from the discharge fluid path 423. In this case, apart of the target substances are adhered to the surface of the sensorchip 300 (an electrical conductor).

The discharge fluid path 423 for guiding the gaseous sample to theoutlet duct 410 may be connected to fluid path 422 (in the broadestsense, the guide unit 420) near the sensor chip 300. In the example inFIG. 3A, the discharge fluid path 423 and the fluid path 422 areconnected through a connector 490 such as a flange or a coupler.

The sensor chip 300 can enhance the Raman scattering light generated byreceiving the light from the light source A, and the fluid path of theguide unit 420 may be improved in order to increase a possibility thatthe gaseous sample is attached to or adsorbed on the surface of thesensor chip 300. In a simple fluid path (not shown), the gaseous samplemay pass through the sensor chip 300. Therefore, the guide unit 420 mayhave a fluid path such that the gaseous sample is circulated around thevicinity of the surface of the sensor chip 300. The circulated gaseoussample is difficult to directly go to the outlet duct 410 or thedischarge fluid path 423 and may stay in the fluid path 422 near thesensor chip 300.

As shown in FIG. 3A, the gaseous sample can be circulated in the fluidpath 422 (the second fluid path) in the vicinity of the sensor chip 300.Due to the generation of rotating flow, the possibility in which thegaseous sample is entering the sensor chip 300 improves. Therefore, thesignal intensity of the Raman scattering light becomes stable, and evenin the case where the amount of the gaseous sample is small the gaseoussample (target substance) can be easily detected or specified.

As the target substance trace molecules such as a narcotic drugs,alcohol, or residual pesticides or pathogenic agents such as viruses maybe envisaged.

Preferably, a possibility that the gaseous sample makes contact with thesurface of the sensor chip 300 is high. Furthermore, the external light(not shown) does not reach the sensor chip 300 as long as possible. Asshown in FIG. 3A, the inlet fluid path 421 (first fluid path) of theguide unit 420 may have a reflecting structure. By reducing a ratio ofthe external light (noise) to the Raman scattering light (signal), it ispossible to improve the signal-to-noise (S/N) ratio to detect the Ramanscattering light, and thus, to enhance the detection sensitivity.

If the inlet fluid path 421 is straight, it is difficult to block theexternal light in the inlet fluid path 421, so that the detectionsensitivity may be degraded.

The example in FIG. 3D illustrates an optical path when the externallight reaches the fluid path 422 in the vicinity of the sensor chip 300through the inlet fluid path 421. For example, as shown in FIG. 3D, theexternal light is reflected by the inner wall of the inlet fluid path421 three times. The inlet fluid path 421 has an inner wall surface forblocking the incident rays of the external light between the inlet duct400 (import hole) and the sensor chip 300. Through such a reflectingstructure, the inlet fluid path 421 is provided with a light-blockingproperty.

Although the inlet fluid path 421 has a reflecting structure in theexample in FIG. 3A, the inner wall of the inlet fluid path 421 ispreferably curved such that the resistance of the fluid path is reduced.In addition, the inner wall of the inlet fluid path 421 is preferablymade of a material having a low light reflectance to increase the lightblocking property. Furthermore, the discharge fluid path 423 (thirdfluid path) of the guide unit 420 also preferably has a structurecapable of increasing the light blocking property.

The example in FIG. 3D illustrates an optical path (incident rays) whenthe external light reaches the fluid path 422 near the sensor chip 300through the discharge fluid path 423. For example, as shown in FIG. 3D,the external light is reflected 3 times by the inner wall of thedischarge fluid path 423. The discharge fluid path 423 has an inner wallsurface for blocking the incident rays of the external light between theoutlet duct 410 and the sensor chip 300. Through such a reflectingstructure, the discharge fluid path 423 may be provided with the lightblocking property.

In the example in FIG. 3A, the inlet fluid path 421 (in the broadestsense, guide unit 420, and in broadest possible sense, the opticaldevice unit) may include a filter 426 (for example, the dust-removingfilter) for removing dust in the air. The filter 426 preferably blocksthe external light, and may serve as both the dust-removing filter andthe light-blocking filter. In addition, the discharge fluid path 423 (inthe broadest sense, the detection apparatus) may also include a filter427 (for example, a light-blocking filter) for blocking the externallight.

In the example in FIG. 3A, the detection apparatus includes a covering440, and the covering 440 may store a sensor chip 300. In addition, thedetection apparatus includes a casing 500, and the light source A, thehalf mirror 2, the object lens 3, and the detector 5 may be included inthe casing 500. The detector 5 includes a spectroscopic element 370 andan optical receiver element 380. The spectroscopic element 370 mayinclude etalon. Furthermore, the detection apparatus may include acondensing lens 360, an optical filter 365, a processing unit 460, apower supply unit 470, a communication connection plug 510, and a powerconnection plug 520.

In the example in FIG. 3A, the detection apparatus has a hinge 480, andthe covering 440 can be opened/closed through the hinge 480. While thecovering 440 is opened, the used optical device unit may be removed.Alternatively, as shown in FIG. 3B, while the covering 440 is opened, anew optical device unit may be integrated into the detection apparatus.In addition, the detection apparatus has a latching portion (not shown),and the optical device unit has a latched portion (not shown)corresponding to the latching portion so that the optical device unitcan be positioned. In addition, the sensor chip detection element 310may detect whether or not the sensor chip 300 (in the broadest sense,optical device unit) is suitably integrated into the detectionapparatus. FIG. 3C illustrates an optical device unit for exchange, andthe optical device unit may have encapsulation members 424 and 425 toprevent contamination of the guide unit 420 and the sensor chip 300. Theoptical device unit may have an identification code 305 (for example, abard code) for identifying the sensor chip 300, and the sensor chipdetection element 310 (for example, a barcode reader) may read theidentification code 305.

In the example in FIG. 3A, the detection apparatus further includes apolarization control element 330 and a collimator lens 320 correspondingto the light source A. The light emitted from the light source A iscollimated by the collimator lens 320 and plane-polarized by thepolarization control element 330. In addition, if a surface-emittinglaser is employed as the light source to allow the plane-polarized lightto be emitted, it is possible to omit the polarization control element330.

The light from the light source A is attracted to the direction of thesensor chip 300 by the half mirror 2 (dichroic mirror), condensed to theobject lens 3, and is incident to the sensor chip 300. For example, ametal nano-structure is formed on the surface of the sensor chip 300.From the sensor chip 300 Rayleigh scattering light and Raman scatteringlight are emitted from the sensor chip 300 by surface-enhanced Ramanscattering. The Raman scattering light and the Rayleigh scattering lightfrom the sensor chip 300 pass through the object lens 3 and areattracted to the direction of the detector 5 by the half mirror 2.

In the example in FIG. 3A, the light from the light source A reaches thefront surface of the sensor chip 300 from the rear surface thereof, andthe Rayleigh scattering light and the Raman scattering light aregenerated from the vicinity of the metal nano-structure, so that theRayleigh scattering light and the Raman scattering light are radiatedfrom the rear surface of the sensor chip 300 (refer to FIG. 2E). Inaddition, the arrangement of the sensor chip 300 in FIG. 3 may bechanged such that the light from the light source A directly reaches thefront surface of the sensor chip 300 (refer to FIG. 2D).

In the example in FIG. 3A, the Rayleigh scattering light and the Ramanscattering light from the sensor chip 300 are condensed by thecondensing lens 360 and reach the optical filter 365. In addition, theRaman scattering light is extracted by the optical filter 365 (forexample, a notch filter), and the optical receiver element 380 receivesthe Raman scattering light through the spectroscopic element 370. Thewavelength of the light passing through the spectroscopic element 370can be controlled (selected) by the processing unit 460.

The optical receiver element 380 receives the Raman scattering lightthrough the optical system and the spectroscopic element 370. Theoptical system (second optical system) includes a half mirror 2, acondensing lens 360, and an optical filter 365. A Raman spectrum uniqueto the target substance is obtained by the spectroscopic element 370 andthe optical receiver element 380, and the target substance can bespecified by checking the obtained Raman spectrum against thepreviously-stored data.

In the example in FIG. 3A, the processing unit 460 may turn on/off thepower of the light source A. For example, the processing unit 460 maycarry out the function of the control unit 7 shown in FIG. 1B, and theprocessing unit 460 may variably control the position of the lightsource A. In addition, the processing unit 460 may send instructions tothe detector 5 and the fan 450 other than the light source A shown inFIG. 3A, and the processing unit 460 may control the detector 5 and thefan 450 as well as the light source A. In addition, the processing unit460 may carry out the spectroscopic analysis using the Raman spectrum,and the processing unit 460 may specify the target substance. Inaddition, the processing unit 460 may transmit the detection result ofRaman scattering light, the spectroscopic analysis result of the Ramanspectrum is transmitted to an external device (not shown) connected tothe communication connection plug 510.

In the example in FIG. 3A, the power supply unit 470 may supply power tothe light source A, the detector 5, the fan 450, the processing unit 460shown in FIG. 3A. The power supply unit 470 may be configured using asecondary battery as well as a primary battery and an AC adaptor. In acase where the power supply unit 470 is configured using the secondarybattery, an electric charger (not shown) connected to the powerconnection plug 520 may charge the secondary battery. In a case wherethe power supply unit 470 is configured using an AC adaptor, the ACadaptor is arranged in an external side of the detection apparatus andconnected to the power connection plug 520. In addition, the detectionapparatus may include a display unit (the display unit 540 in theexample in FIG. 4), and the display unit may display the state of thepower supply unit 470 (for example, out of battery, now charging,charging completed, power is being supplied).

FIG. 4 illustrates an exemplary block diagram of the detection apparatusof FIG. 3A. In the following description, like reference numerals denotelike elements as in FIG. 3A, and description thereof will not berepeated. As shown in FIG. 4, the detection apparatus may furtherinclude a display unit 540, a manipulation unit 550, and an interface530. In addition, the processing unit 460 shown in FIG. 3A may include acentral processing unit (CPU) 461, random access memory (RAM) 462, andread only memory (ROM) 463. Furthermore, the detection apparatus mayinclude a light source driver 15, a spectroscopic driver 375, an opticalreceiver circuit 385, and a fan driver 455. Hereinafter, an operationalexample of the detection apparatus shown in FIG. 4 will be described.

In the example in FIG. 4, the CPU 461 may determine whether or notpreparation to detect the Raman scattering light has been completed, andthe CPU 461 may send a signal indicating that the preparation has beencompleted to the display unit 540. In addition, the CPU 461 may sendsignals other than that signal to the display unit 540. The display unit540 may provide a user with various display contents in response to thesignal (display signal) from the CPU 461.

In the example in FIG. 4, the detection circuit 315 may extract theidentification code 305 detected by the sensor chip detection element310 as an electrical signal. The CPU 461 may receive the electric signalin a digital format and specify the type of the sensor chip 300 using avalue thereof. Then, the CPU 461 may recognize that it is ready todetect the Raman scattering light.

In a case where the display unit 540 indicates that it is ready todetect the Raman scattering light, a user manipulates the manipulationunit 550 to initiate the detection of the Raman scattering light. In acase where the signal from the manipulation unit 550 (manipulationsignal) initiates detection, the CPU 461 may actuate the light source Athrough a light source driver 15. Specifically, the light source driver15 (in the broadest sense, the CPU 461) may power on the light source A.In addition, the light source A may include a temperature sensor (notshown) and a light amount sensor (not shown). The light source A maysend the temperature and the light amount of the light source A to theCPU 461 through the light source driver 15. The CPU 461 may receive thetemperature and the light amount of the light source A and determinewhether or not the output of the light source A is stable. While thelight source A is powered on, and after the output of the light source Abecomes stable in some cases, the CPU 461 may actuate the fan 450through the fan driver 455.

In addition, the CPU 461 (in the broadest sense, the processing unit460) may carry out the function of the control unit 7 shown in FIG. 1B,and may variably control the position of the light source A through thelight source driver 15. Alternatively, the CPU 461 may variably controlthe position of the object lens 3 shown in FIG. 1D through the lightsource driver 15 or the lens driver (not shown).

In the example in FIG. 4, the fan driver 455 may power on the fan 450.As a result, the target substance (gaseous sample) is suctioned into theguide unit 420 in FIGS. 3A to 3D. In a case where the light source A inFIG. 3A is powered on, the light from the light source A reaches thesensor chip 300 in FIGS. 3A to 3D through the half mirror 2. Inresponse, the Rayleigh scattering light and the Raman scattering lightare returned to the half mirror 2 from the sensor chip 300. The Rayleighscattering light and the Raman scattering light from the sensor chip 300arrive at the optical filter 365 through the condensing lens 360. Theoptical filter 365 blocks the Rayleigh scattering light and guides theRaman scattering light to the spectroscopic element 370. Theaforementioned process can be made using a fan 450 when the fluid pathresistance from the inlet duct 400 (a loading entrance) to the guideunit 420 and the outlet duct 410 is relatively small. However, when thefluid path resistance is relatively large, a suction pump (not shown)may be used instead of the fan 450.

In the example in FIG. 4, the spectroscopic driver 375 (in the broadestsense, the CPU 461) may control the spectroscopic element 370. Thespectroscopic element 370 may be made of a variable etalon spectroscopecapable of changing the resonance wavelength. In a case where thespectroscopic element 370 is an etalon using Fabry-Perot resonance, thespectroscopic driver 375 may change (select) the wavelength of the lightpassing through the etalon while the distance between the two facingetalon plates is adjusted. Specifically, when the wavelength of thelight passing through the etalon is set to a range from the firstwavelength to the Nth wavelength, first, the distance between the twoetalon plates is set such that the light of the first wavelengthrepresents a maximum intensity. Then, the distance between the twoetalon plates is set again such that the light having a secondwavelength deviated by a half maximum full width from the firstwavelength has a maximum intensity. In such a method, the light passingthrough the etalon is received by the optical receiver element 380 whilethe first wavelength, the second wavelength, the third wavelength, . . ., and the Nth wavelength are sequentially selected.

In the example in FIG. 4, the optical receiver circuit 385 (in thebroadest sense, the CPU 461) may extract the light received from theoptical receiver element 380 as an electric signal. The CPU 461 receivesthe electric signal in a digital format and stores the value thereof inthe RAM 462. Since the spectroscopic element 370 selectively guides thelight in a range of the first wavelength to the Nth wavelength to theoptical receiver element 380, the CPU 461 can store the Raman spectrumin the RAM 462 in a digital format.

In the example in FIG. 4, the CPU 461 may compare the Raman spectraldata unique to the target substance stored in the RAM 462 with theexisting Raman spectral data stored in advance in the ROM 463. The CPU461 may determine what kind of material the target substance is based onthe comparison result. The CPU 461 may send a signal indicating thecomparison result or the determination result to the display unit 540.As a result, the display unit 540 may notify a user of the comparisonresult or the determination result. In addition, the CPU 461 may outputthe data indicating the comparison result or the determination resultfrom the communication connection plug 510. The interface 530 maytransmit/receive data to/from an external device (not show) connected tothe CPU 461 and the communication connection plug 510 according to apredetermined standard.

In the example in FIG. 4, the CPU 461 may determine the state of thepower supply unit 470. In a case where the power supply unit 470includes the primary battery or the secondary battery, the CPU 461 maydetermine whether or not the data indicating a voltage of the primarybattery or the secondary battery are equal to or smaller than apredetermined value previously stored in the ROM 463. The CPU 461 maytransmit the signal indicating the determination result to the displayunit 540. As a result, the display unit 540 may allow a user to see thedetermination result (for example, out of battery, charging required) oran instruction based on the determination result. In addition, in a casewhere the power supply unit 470 includes the secondary battery, the CPU461 may determine whether or not the secondary battery is being charged.

In the example in FIG. 4, the power supply unit 470 may transmit thestate of the power supply unit 470 to the CPU 461. In addition, thepower supply unit 470 may supply power to the processing unit 460including the CPU 461. Although not shown in FIG. 4, the power supplyunit 470 may supply power to the components of the detection apparatussuch as the light source driver 15, the optical receiver circuit 385,and the light source group 1.

2.2. Light Source

FIGS. 5A and 5B illustrate a configuration example of a VCSEL. In theexample in FIG. 5A, an n-type DBR (Diffracted Bragg Reflector) layer isformed on an n-type GaAs substrate. An active layer and an oxidationconstriction layer are provided at the center of the n-type diffractedBragg reflector (DBR) layer. A p-type DBR layer is provided on theactive layer and the oxidation constriction layer. An electrode isformed on the insulation layer by providing an insulation layer on thep-type DBR layer and the n-type DBR layer. The electrode is also formedon the rear side of the n-type GaAs substrate. In the example in FIG.5A, an active layer is interposed between the n-type DBR layer and thep-type DBR layer, so that a vertical resonator is formed, in which thelight generated from the active layer is resonated between the n-typeDBR layer and the p-type DBR layer. In addition, the VCSEL is notlimited to the example in FIG. 5A. For example, the oxidationconstriction layer may be omitted.

For example, the light source A shown in FIG. 1A is preferably a VCSEL(in the broadest sense, surface-emitting laser) capable of emittinglight to a direction perpendicular to the substrate surface (the opticalaxis Lax1 of the light source) by resonating the light in a directionperpendicular to the substrate surface. By using the VCSEL, it ispossible to configure a light source which is monochromic (singlewavelength) and plane-polarized. In addition, the VCSEL can beminiaturized and suitable for incorporating into a portable detectionapparatus. In addition, from the structure of the VCSEL, it is possibleto form a resonator without cleaving the substrate during themanufacturing process and inspect the characteristics of laser, which issuitable for mass production. Furthermore, the VCSEL can be manufacturedwith lower cost than those of other semiconductor laser devices, and2-dimensional array type VCSEL can be provided as well. Furthermore,since the threshold current of the VCSEL is small, it is possible toreduce power consumption in the detection apparatus. In addition, it ispossible to modulate the VCSEL in a high speed even using a low electriccurrent, and reduce the width of the characteristic change for thetemperature change of the VCSEL. In addition, it is possible to simplifythe temperature control unit of the VCSEL.

By modifying the example in FIG. 5A, the VCSEL can provide a stablepolarization surface (in the broadest sense, a polarization direction).In this case, instead of the polarization control element 330 in FIG. 3Athe light source A (vertical cavity surface-emitting laser) may have adistorting portion as disclosed in Japanese Patent No. 3482824. In theexample disclosed in Japanese Patent No. 3482824, the distorting portion19 is disposed in the vicinity of the resonator 10B of the VCSEL.According to Japanese Patent No. 3482824, the distorting portion 19generates birefringence and dependence on polarization of the gainwithin the resonator 10A by distorting the anisotropic stress to theresonator 10B. As a result, it is possible to provide a stablepolarization surface.

In the example in FIG. 5B, a plan view of the VCSEL is illustrated, inwhich the light source A has a distorting portion. In the example inFIG. 5B, the light source A can radiate light having a polarizationdirection DA.

FIG. 6 is an explanatory diagram illustrating a characteristic of lightsources. In the example in FIG. 6, characteristics of lasers that can beused in the light source are represented as a table. Although a VCSEL issuitable for the light source of the detection apparatus as describedabove, the detection apparatus may employ other kinds of laser asillustrated in FIG. 6, or light sources other than the laser.

2.3. Guide Unit

FIGS. 7A to 7C illustrate an exemplary configuration of the guide unitand the discharge fluid path 423. As shown in FIG. 7A, the fluid path422 in the vicinity of the sensor chip 300 may have a cylindricalstructure. The cylindrical structure includes an inner peripheralsurface 422 a and a plane 422 b perpendicular to the inner peripheralsurface 422 a so that the gaseous sample can be rotated in a direction(horizontal direction) parallel to the plane (in the broadest sense,virtual plane) of substrate 100 (in narrow meaning, the electricalconductor) on the inner peripheral surface 422 a (wall surface).Rotation of the gaseous sample in a direction parallel to the virtualplane (for example, horizontal cross-sectional surface) of theelectrical conductor may be called horizontal rotation or transversalrotation. The inlet of the fluid path 422 in the vicinity of the sensorchip 300 is connected to the outlet of the inlet fluid path 421, and theoutlet of the fluid path 422 in the vicinity of the sensor chip 300 isconnected to the inlet of the discharge fluid path 423. The inflowdirection of the gaseous sample to the inlet of the fluid path 422 fromthe outlet of the inlet fluid path 421 is approximated to a directionparallel to the plane 422 b, so that the gaseous sample is apt to rotatein a horizontal direction. In addition, as shown in FIG. 7A, a rotatingflow in a horizontal direction may be mainly generated, and a rotatingflow in a vertical direction may be generated. The gaseous sample staysin the vicinity of the sensor chip 300, and then, is discharged from thedischarge fluid path 423. Since the gaseous sample passes through thevicinity of the enhanced electric field near the sensor chip 300 severaltimes, a possibility that the gaseous sample enters the enhancedelectric field increases.

As shown in FIG. 7B, the fluid path 422 near the sensor chip 300 mayhave a cavity-shaped structure. The cavity-shaped structure has an innerspherical surface 422 c. The gaseous sample can be rotated in adirection (vertical direction) perpendicular to the virtual plane of theelectrical conductor on the inner spherical surface 422 c (wallsurface). Rotation of the gaseous sample in a direction perpendicular tothe virtual plane (for example, a horizontal cross section) of theelectrical conductor may be called vertical rotation or longitudinalrotation. Since the inflow direction of the gaseous sample from theoutlet of the inlet fluid path 421 to the inlet of the fluid path 422 isapproximated to a direction perpendicular to the plane 422 b, thegaseous sample is apt to rotate in a vertical direction. In addition, asshown in FIG. 7B, the rotation flow in a vertical direction is mainlygenerated, and the rotation flow in a horizontal direction may begenerated.

In the example in FIG. 7C, the inlet fluid path 421 may have a helicalstructure. The gaseous sample enters the fluid path 422 from the inletfluid path 421. In this case, since the inlet fluid path 421 has ahelical structure, a rotating gaseous sample enters the fluid path 422.Therefore, since the gaseous sample may further rotate in the fluid path422, a possibility that the gaseous sample stays in the enhancedelectric field near the electric conductor further increases. Inaddition, the inlet fluid path 421 can block the external light, and theinner wall of the inlet fluid path 421 is preferably made of a materialhaving low light reflectivity to increase the light blocking property.In the example in FIG. 7C, the guide unit 420 (in the broadest sense,optical device unit) may have a relay path 423 a connectable to thedischarge fluid path 423.

The discharge fluid path 423 may have a helical structure as shown inFIG. 7C. In addition the inlet fluid path 421 shown in FIG. 7A may havea helical structure.

2.4. Optical Device (Metal Nano-Structure According to aPhotolithographic Technique)

FIGS. 8A to 8E are schematic explanatory diagrams illustrating aphotolithographic technique. In the example in FIG. 8A, an opticalinterferotype exposure apparatus using ultraviolet laser isschematically illustrated, and continuous wave (CW) laser having awavelength of 266 nm and an output power of 200 mW may be used as thelight source. The light from the ultraviolet laser is reflected at themirror via a shutter and splits into both sides of the half mirror. Thetwo light beams split from the half mirror are reflected at the mirrorand pass through the object lens and the pinhole so that the diametersof the light beams are enlarged. An exposure pattern may be formed byirradiating the light from the ultraviolet laser having an enlarged beamdiameter onto a mask, and the exposure pattern may be irradiated ontothe substrate 100 where a photoresist has been coated. In this case,since the exposure patterns from both masks are interfered with eachother, an interference pattern can be formed on the photoresist(substrate 100). In addition, it is possible to recognize the exposurepattern on a monitor using a half mirror or a CCD camera.

After a predetermined interference pattern (in the broadest sense, apredetermined exposure pattern) is exposed on the photoresist (substrate100), it is possible to leave only a desired part of the photoresist bydeveloping the photoresist. Then, the substrate 100 may be etched to asmuch as the necessary amount by immersing it into an etching solution orthrough dry etching. After the etching, the photoresist remaining on thesubstrate 100 may be removed. As a result, it is possible to manufacturethe surface of the substrate 100 in a fine embossed shape. Then, it ispossible to form a metal nano-structure by adding metal fine-particlesas an electrical conductor on the surface of the substrate 100. Anoverview of the manufacturing process of the metal nano-structure willbe described below (refer to FIGS. 9A to 9E).

In the example in FIG. 8B, a substrate 100 having a metal nano-structureis illustrated in a plan view and a cross-sectional view. In thisexample, the substrate 100 (metal nano-structure) includes a protrusiongroup 115 including a plurality of protrusions 110, and a plurality ofprotrusions 110 (metal fine-particles 20) are periodically arranged in aone-dimensional space.

Also in the example in FIG. 8C, the substrate 100 having a metalnano-structure is illustrated in a plan view and a cross-sectional view.In this example, a plurality of protrusions 110 (metal fine-particles20) are periodically arranged in a two-dimensional space. In the examplein FIG. 8D, the substrate 100 having a metal nano-structure isillustrated as an electron microscope photograph in a perspective viewand corresponds to FIG. 8C. In the example in FIG. 8D, the substrate 100having a metal nano-structure is illustrated in a plan view as ascanning electro microscopy (SEM) photograph, and corresponds to FIG.8C. For example, a period (pitch) of a plurality of protrusions 110containing gold (Au) is set to approximately 140 nm.

In addition, the metal nano-structure may be formed using an electronbeam exposure apparatus instead of the optical interferotype exposureapparatus. While the electron beam exposure apparatus is advantageous inview of a higher exposure freedom in comparison with the opticalinterferotype exposure apparatus, the optical interferotype exposureapparatus is advantageous in view of higher productivity of the opticaldevice in comparison with the electron beam exposure apparatus.

FIGS. 9A to 9E are schematic explanatory diagrams illustrating amanufacturing process of the metal nano-structure. In the followingdescription, like reference numerals denote like elements as in FIG. 8B,and description thereof will not be repeated. For example, the metalnano-structure illustrated in FIG. 8C may be manufactured, specifically,as described below. As shown in FIG. 9A, the substrate 100 has aphotoresist 101. The photoresist 101 is coated on the substrate 100using a spin coat, and then, dried. In order to expose the predeterminedpattern on the photoresist 101 an optical interferotype exposureapparatus as shown in FIG. 8A may be used. For example, a positivephotoresist may be used as the photoresist 101, and the thickness of thephotoresist 101 may be set to 1 μm. In the example in FIG. 9A, the lightbeams from two directions are irradiated onto the photoresist 101, andeach of the two light beams has an exposure pattern having a latticeshape. It is possible to form various interference patterns using acrossing angle between the two light beams. In addition, the size of theinterference pattern may be reduced to a half of the wavelength of theultraviolet laser in the optical interferotype exposure apparatus. Alatent image generated by the interference pattern is formed in thephotoresist 101, and the photoresist 101 is developed. As a result, itis possible to form a photoresist pattern as shown in FIG. 9B.

As shown in FIG. 9B, the substrate 100 includes a portion protected bythe photoresist pattern and a portion unprotected by the photoresistpattern. Then, the portion unprotected by the photoresist pattern isetched to form a concave portion 104 in the substrate 100 as shown inFIG. 9C. Then, by removing the photoresist 101 remaining in thesubstrate 100 the convex portion 105 of the substrate 100 shown in FIG.9D is exposed. Then a metal film containing metal fine-particles 20 isformed on the substrate 100 using a sputtering apparatus. Although athin metal film is formed on the entire area of the substrate 100 in aninitial state, a lot of metal fine-particles 20 are gradually adhered inthe vicinity of the convex portion 105 so that a plurality ofprotrusions 110 (metal nano-structure) can be formed in the metal filmas shown in FIG. 9E.

If plane-polarized laser light is irradiated onto the protrusion group115 including a plurality of protrusions 110 (the metal nano-structure),localized plasmons are excited by the polarization direction of thelaser light, and a strong enhanced electric field is formed in the gapbetween the neighboring protrusions 110 in the protrusion group 115. Thegap between the neighboring protrusions 110 in the protrusion group 115can be controlled using the thickness of the metal film. The size of thegap serves as a main factor for controlling the strength of the enhancedelectric field.

The metal fine-particle 20 or the metal film may be formed of aurum(gold) (Au), silver (Ag), copper (Cu), aluminum (Al), palladium (Pd),platinum (Pt), or alloy thereof (a combination thereof). Preferably, themetal fine-particles 20 or the metal film may be formed of gold (Au) orsilver (Ag) to make it easier to generate the localized plasmon, theenhanced electric field, or the surface-enhanced Raman scattering.

FIGS. 10A to 10C are schematic explanatory diagrams illustrating theenhanced electric field formed from the metal nano-structure. In thefollowing description, like reference numerals denote like elements asin FIG. 2D, and description thereof will not be repeated. The targetmolecule (gaseous sample) is suctioned to the inner side of the guideunit 420 from the inlet duct 400 as shown in FIG. 3A and reaches thefluid path 422 in the vicinity of the sensor chip 300 (in the broadestsense, the optical device 4). In the example in FIG. 10A, the opticaldevice 4 includes a metal nano-structure. If the light Lin (incidentlight) is irradiated from the light source to the metal nano-structure,the enhanced electric field is formed in the gap of the convex portion105. In the example in FIG. 10B, an irradiation range of the light Lin(incident light) is illustrated as a dotted line. In addition, in a casewhere the target molecule enters the enhanced electric field, the Ramanscattering light is generated including information on the frequency ofthe target molecule. In addition, the Raman scattering light is enhancedby the enhanced electric field, and the surface-enhanced Ramanscattering is generated. Although the incident light is irradiated fromthe rear side (the substrate 100 side) of the optical device 4 in theexample in FIG. 10A, the incident light may be irradiated from thesurface side of the sensor chip 300 (the convex portion 105 side), asshown in FIG. 10C.

If the gap between the convex portions 105 becomes small and the heightof the convex portion 105 (the depth of the concave portion 104) becomeslarge, generally, the enhanced electric field shown in FIG. 10A becomesstrong. In addition, as the intensity of the light Lin (incident light)becomes higher, the enhanced electric field becomes strong. However, ifthe gap between the convex portions 105 is too narrow, the probabilityin which the target molecule enters the gap (enhanced electric field)becomes low. Therefore, the gap between the convex portions 105 can beset to several nm to several tens nm, for example. Further, if theheight of the convex portion 105 (the depth of the concave portion 104)becomes large, the time in which the target molecule exits from the gap(enhanced electric field) after entering the gap (enhanced electricfield) can be increased, and the detection signal or the Raman spectrumrepresenting the Raman scattering light becomes stable.

In addition, the wavelength of the light Lin (incident light) may beselected based on the type of the metal of the metal nano-structure. Ina case where the metal nano-structure is formed of gold (Au), thewavelength of the light Lin may be set to 633 nm. In addition, in a casewhere the metal nano-structure is formed of silver (Ag), the wavelengthof the light Lin may be set to 514 nm. In addition, it is possible toselect the wavelength of the light Lin depending on the type of thetarget molecule. In addition, in a case where the gaseous samplecontains impurities other than the target molecule, the wavelength ofthe light Lin may be set to 780 nm in order to suppress fluorescence ofthe impurities.

2.5. Surface Plasmon Resonance Peak

When the light Lin (incident light) is irradiated onto the metalnano-structure (in the broadest sense, an electrical conductor) of theoptical device 4 illustrated in FIG. 10C, typically, only a single broadsurface plasmon resonance peak exists. Therefore, it is necessary to setthe position of the resonance peak to a suitable position inconsideration of the excitation wavelength (equal to the Rayleighscattering wavelength) and the Raman scattering wavelength. Therefore,if the resonance peak wavelength is set to a value between theexcitation wavelength and the Raman scattering wavelength, it ispossible to anticipate the electric field enhancement effect in both theexcitation process and the Raman scattering process. However, since theresonance peak is broad, the intensity of the resonance is reduced inindividual processes, and it can be said that the enhancement degree ofthe entire process is not sufficient. In this regard, it is possible toimprove the detection sensitivity and the sensor sensitivity byintroducing the incident light to the optical device 4 with aninclination to generate two resonance peaks and setting the tworesonance peaks as the excitation wavelength and the Raman scatteringwavelength.

In order to implement a high-sensitivity sensor chip 300 (in thebroadest sense, the optical device 4) by applying the surface-enhancedRaman scattering, it is preferable that the enhancement degree of thelocal electric field (hereinafter, simply referred to as an enhancementdegree) increases as large as possible. The enhancement degree α can beexpressed as the following Equation (1) (M. Inoue, K. Ohtaka, J. Phys.Soc. Jpn., 52, 3853 (1983). In the Equation (1), αray denotes anenhancement degree using the excitation wavelength, and αram denotes theenhancement degree using the Raman scattering wavelength.α=αray×αram  (1)

Based on the Equation (1) described above, it is possible to increasethe enhancement degree in the course of the surface-enhanced Ramanscattering by simultaneously increasing both the enhancement degree inthe excitation process and the enhancement degree in the Ramanscattering process. Therefore as shown in FIG. 11, it is possible togenerate two resonance peaks that are strong only in the vicinity of theexcitation wavelength and the Raman scattering wavelength. As a result,it is possible to increase the enhancement effect of the local electricfield by a synergy effect of both scattering processes.

FIG. 12 is a perspective view illustrating a configuration example ofthe sensor chip. As shown in FIG. 12, the sensor chip 300 includes asubstrate 100 (base material) and a protrusion group 115 (a firstprotrusion group). The protrusion group 115 having a plurality ofprotrusions 110 contains an electrical conductor, and the electricalconductor is typically formed of metal (for example, gold (Au)) or maybe formed of a semiconductor (for example, poly-silicon).

A plurality of protrusions 110 are periodically arranged in the firstdirection D1 along the plane of the substrate 100 (in the broadestsense, a virtual plane). Here, the plane of the substrate 100 is thesurface 120 of the substrate 100 where the protrusion group 115 isformed, and may be a plane parallel to the surface 120. Morespecifically, each protrusion 110 of the protrusion group 115 is formedto have a convex shape from the surface 120 of the substrate 100 in across-sectional shape of the arrangement direction of the protrusions(first direction D1). The convex shape may include a rectangular shape,a trapezoidal shape, a circular arc shape. For example, across-sectional shape defined by complicated curves as shown in FIGS. 8Dand 9E may be used. For example, as shown in FIG. 12, the protrusiongroup 115 is formed to have a parallel stripe shape in the seconddirection D2 perpendicular to the first direction D1 as seen in a planview for the substrate 100.

FIG. 13 is a cross-sectional view illustrating a sensor chip in FIG. 12.The cross section of this cross-sectional view is perpendicular to theplane of the substrate 100 and parallel to the arrangement direction ofthe protrusion group 115 (first direction D1). As shown in FIG. 13, thedirection normal to the plane of the substrate 100 is set to a thirddirection D3.

In the example in FIG. 13, the substrate 100 has a glass substrate 130and a metal thin film 140 formed on the glass substrate 130. Forexample, the metal thin film 140 has a thickness equal to or larger than150 nm. In the example in FIG. 13, the cross-sectional shape of theprotrusion group 115 is rectangular (approximately rectangular), and theprotrusions 110 having a first height H1 are arranged with a firstperiod P1 along the first direction D1. A metal lattice 150(periodically embossed metal structure) is formed by the metal thin film140 and the protrusion group 115. The first period P1 is preferably setto a range between 100 and 1000 nm, and the first height H1 ispreferably set to a range between 10 and 100 nm. In addition, the glasssubstrate 130 may be substituted with a quartz substrate, a sapphiresubstrate. The substrate 100 may be formed using a metal plate.

The incident light Lin including plane polarization may be incident tothe sensor chip 300. The direction (polarization orientation) of theplane polarization is parallel to the surface parallel to the firstdirection D1 and the third direction D3. In the example in FIG. 13, theincident light Lin is incident with an inclination with respect to themetal lattice 150 including the metal thin film 140 and the protrusiongroup 115 (in the broadest sense, an electrical conductor).Specifically, if the inclination angle is set to θ, θ>0. The incidentlight is incident such that an angle between the direction incident tothe cross section in FIG. 13 and the direction opposite to the thirddirection D3 (an angle with respect to the normal line directed to theplane of the substrate 100) becomes θ.

Preferably, the plane polarization is parallel to the surface parallelto the first direction D1 and the third direction D3. However, the planepolarization may be nonparallel to the plane parallel to the firstdirection D1 and the third direction D3. In other words, the planepolarization may contain a polarization component parallel to thesurface parallel to the first direction D1 and the third direction D3.In addition, the polarization direction of the plane polarization may beset by the distorting portion in FIG. 5B, the polarization controlelement 330 in FIG. 3A.

FIG. 14 illustrates an exemplary characteristic of the reflective lightintensity of the sensor chip. FIG. 14 illustrates an exemplarycharacteristic in the event that the metal lattice 150 is formed ofsilver Ag, the incident angle θ of the light for the metal lattice 150is set to 3°, the polarization direction of the light is perpendicularto the groove direction of the metal lattice 150 (second direction D2),the cross section of the protrusion 110 has a rectangular shape(approximately rectangular), the first period P1 is set to 500 nm, andthe first height H1 is set to 20 nm. In the example in FIG. 14, theabscissa denotes the wavelength of the reflective light, and theordinate denotes the reflective light intensity (a ratio with respect tothe incident light intensity).

In the example in FIG. 14, two resonance peaks of the surface plasmonpolaritons (SPP) exist in the metal lattice 150. For example, a singleresonance peak wavelength λp1 is positioned in the vicinity of 515 nm,and the other resonance peak wavelength λp2 is positioned in thevicinity of 555 nm. It is possible to obtain a significant enhancedRaman scattering effect by matching or adjusting the two resonance peakwavelengths λp1 and λp2 to the vicinity of the excitation wavelength λ1and the Raman scattering wavelength λ2, respectively. For example, in acase where Argon laser having a wavelength of 515 nm is used as theexcitation wavelength λ1, it is possible to strongly enhance the Ramanscattering light in the vicinity of a wavelength of 555 nm (Raman shiftof 1200 to 1600 cm⁻¹).

FIG. 15 is an explanatory diagram illustrating an excitation conditionof the surface plasmon polaritons. The reference numeral C1 in FIG. 15denotes a distribution curve of the surface plasmon polaritons (forexample, a distribution curve at the interface between the air and gold(Au)), and the reference numeral C2 denotes a light line. In FIG. 15,the period of the metal lattice 150 is set to a first period P1, and thewave number 2π/P1 of the lattice vector in this case is illustrated onthe abscissa.

First, a relationship between the metal lattice 150 and the excitationcondition will be described. If the wave number of the incident lightLin is denoted by ki, and the incident angle is denoted by θ, the wavenumber of the primary evanescent wave in the arrangement direction ofthe metal lattice 150 (the first direction D1 in FIG. 13 or the oppositedirection of the first direction D1) is set to 2π/P1±ki·sin θ. Thesurface plasmon polaritons are excited when the wave number 2π/P1±ki·sinθ of the evanescent wave and the wave number of the surface plasmonmatch each other. That is, the excitation condition of the surfaceplasmon polaritons is determined by the cross point between the straightline indicating a condition for generating the evanescent wave and adistribution curve of the surface plasmon polaritons.

In C3 in FIG. 15, as a comparison example, a straight line indicating acondition for generating the evanescent wave when light is incidentperpendicularly (θ=0) to the metal lattice 150 is illustrated. As shownin C3, the wave number of the evanescent wave in this case isrepresented as 2π/P1. The straight line C3 is a line extending on theposition of the wave number of the lattice vector, and intersects withthe distribution curve C1 of the surface plasmon polaritons. In thiscase, a single cross point exists, and a resonance peak corresponding tothe frequency ω0 (angular frequency) is generated.

In C4 and C5, a straight line indicating a condition for generating theevanescent wave is illustrated. In a case where light is incident withan angle θ (θ>0) with respect to the metal lattice 150, the wave numberof the evanescent wave can be expressed as 2π/P1±ki±sin θ. The straightline C4 corresponds to 2π/P1+ki·sin θ, and the straight line C5corresponds to 2π/P1−ki·sin θ. Such straight lines C4 and C5 extend fromthe position of the wave number of the lattice vector with aninclination angle θ, and intersect with the distribution curve C1 of thesurface plasmon polaritons at two points (frequencies ω+ and ω−).Therefore, the two resonance peaks corresponding to the frequencies ω+and ω− are represented as resonance peak wavelengths λp1 and λp2.

Two resonance peak wavelengths λp1 and λp2 are set using the excitationcondition of the surface plasmon polaritons, and the two resonance peakwavelengths λp1 and λp2 can be used in the surface-enhanced Ramanscattering. Specifically, first, the distribution curve C1 is obtainedusing a rigorous coupled wave analysis (RCWA) (L. Li and C. W. Haggans,J. Opt. Soc. Am., A10, 1184-1189 (1993)). The distribution curve C1 isunique to the type of the metal, the type of the medium, or across-sectional shape of the metal lattice 150. Then, a predeterminedlattice period (for example, the first period P1) and a predeterminedincident angle θ are determined depending on the Raman shift of thetarget substance. That is, the first resonance peak wavelength λp1 isset in the vicinity of the excitation wavelength λ1 (Rayleigh scatteringwavelength), and the second resonance peak wavelength λp2 (λp2>λp1) isset in the vicinity of the Raman scattering wavelength λ2. In addition,the predetermined first period P1 and the predetermined incident angle θmay be set such that the straight line C4 passes through the cross pointbetween the distribution curve C1 and ω=ω+(λ=λp1), and the straight lineC5 passes through the cross point between the distribution curve C1 andω=ω−(λ=λp2).

In the example in FIG. 14, the first resonance peak wavelength band BW1including the first resonance peak wavelength λp1 includes theexcitation wavelength λ1 in the surface-enhanced Raman scattering. Thesecond resonance peak wavelength band BW2 including the second resonancepeak wavelength λp2 includes the Raman scattering wavelength λ2 in thesurface-enhanced Raman scattering. Since the first period P1 and theincident angle θ are set such that the resonance peak wavelength bandsBW1 and BW2 include the resonance peak wavelengths λ1 and λ2,respectively, it is possible to improve the electric field enhancementdegree in the excitation wavelength λ1 and the electric fieldenhancement degree in the Raman scattering wavelength λ2.

Here, the resonance peak wavelength bands BW1 and BW2 are bandwidths atthe predetermined reflective light intensity, and may be a half-maximumfull width of the peak. In addition, although λ1=λp1 and λ2=λp2 in FIG.14, λ1 may be different from λp1, and λ2 may be different from λp2.

FIG. 16 illustrates another exemplary characteristic of the reflectivelight intensity of the sensor chip. FIG. 16 illustrates an exemplarycharacteristic in the event that the metal lattice 150 is formed of gold(Au), the incident angle θ of the light with respect to the metallattice 150 is set to 5°, the polarization direction of the light isperpendicular to the groove direction of the metal lattice 150 (seconddirection D2), the cross section of the protrusion 110 is rectangular(approximately rectangular), the first period P1 is set to 500 nm, andthe first height H1 is set to 40 nm.

In the example in FIG. 16, a single resonance peak wavelength λp1 ispositioned in the vicinity of 545 nm, and the other resonance peakwavelength λp2 is positioned in the vicinity of 600 nm. It is possibleto obtain a significant enhanced Raman scattering effect by adjusting ormatching the two resonance peak wavelengths λp1 and λp2 in thevicinities of the excitation wavelength λ1 and the Raman scatteringwavelength λ2, respectively.

In the example in FIG. 16, compared to the example in FIG. 14, tworesonance peaks are slightly broad and shallow. However, in comparisonwith the case where only a single resonance peak is used, the effect ofenhancing the signal of the surface-enhanced Raman scattering isexcellent. In addition, it is possible to suppress surface degradationcaused by oxidation and sulfurization by using gold (Au).

FIG. 17 is a perspective view illustrating a modified example of thesensor chip of FIG. 12. Hereinafter, like reference numerals denote likeelements as in FIG. 12, and description thereof will not be repeated. Inthe example in FIG. 12, the incident light Lin is preferablyplane-polarized such that a component parallel to the plane of thesubstrate 100 of the polarization direction (the orthograph with respectto the plane of the substrate 100 of the polarization direction) isparallel to the arrangement direction of the first protrusion group 115(first direction D1). As a result, a compression wave of the freeelectron plasma is generated by the plane polarization along the firstdirection D1, and it is possible to excite the surface plasmonpropagating along the arrangement direction of the first protrusiongroup 115.

In the example in FIG. 17, a second protrusion group 205 formed of metalmay be included on the top surface 220 of the first protrusion group115. Each of a plurality of protrusions 200 of the second protrusiongroup 205 is arranged with a second period P2 (P2<P1) shorter than thefirst period P1 along the direction parallel to the plane of thesubstrate 100 (first direction D1).

In addition, in the example in FIG. 17, a third protrusion group 215formed of metal may be included in the surface between the neighboringprotrusions 110 of the first protrusion group 115 on the surface wherethe first protrusion group 115 is arranged (the bottom surface 230between the neighboring protrusions 110 of the first protrusion group115). Each of a plurality of protrusions 210 of the third protrusiongroup 215 is arranged with a third period P3 (P3<P1) shorter than thefirst period P1 along the direction parallel to the plane of thesubstrate 100 (first direction D1).

As a result, the propagation type surface plasmon is excited by thefirst protrusion group 115, and the localized surface plasmon is excitedby that propagation type surface plasmon in the second protrusion group205 or the third protrusion group 215. As a result, it is possible tofurther improve the electric field enhancement degree in the excitationwavelength λ1 and the Raman scattering wavelength λ2.

The protrusions 200 and 210 of the second protrusion group 205 and thethird protrusion group 215, respectively, are formed such that across-sectional shape in the arrangement direction of the protrusions200 and 210 (first direction D1) has a convex shape from the top surface220 and the bottom surface 230. The convex shape includes a rectangularshape, a trapezoidal shape and a circular arc shape. For example, asshown in FIG. 17, the second protrusion group 205 or the thirdprotrusion group 215 is formed to have a stripe shape parallel to thesecond direction D2 as seen in a plan view with respect to the substrate100. The second protrusion group 205 and the third protrusion group 215may be formed of the same metal as that of the first protrusion group115 or may be formed of other metal materials.

FIG. 18 is a cross-sectional view illustrating the sensor chip of FIG.17. The cross section of FIG. 18 is perpendicular to the plane of thesubstrate 100 and parallel to the first direction D1. As shown in FIG.18, the protrusions 200 having a second height H2 from the top surface220 (the second protrusion group 205) are arranged with a second periodP2 shorter than the first period P1. The protrusions 210 (the thirdprotrusion group 215) having a third height H3 from the bottom surface230 are arranged with a third period P3 shorter than the first periodP1. For example, the second period P2 or the third period P3 ispreferably set to be equal to or shorter than 500 nm, and the secondheight H2 or the third height H3 is preferably set to be equal to orshorter than 200 nm. In addition, the third height H3 may be set to beH3>H1 or H3≦H1.

In the example in FIG. 18, the arrangement direction of the secondprotrusion group 205 or the third protrusion group 215 is the same asthe arrangement direction of the first protrusion group 115 (the firstdirection D1). However, the arrangement direction of the secondprotrusion group 205 or the third protrusion group 215 may be differentfrom the first direction D1. In this case, the second period P2 or thethird period P3 becomes the arrangement period in the first directionD1.

As described above, using the first protrusion group 115, propagationtype surface plasmons having two resonance peaks in the excitationwavelength λ1 (Rayleigh scattering wavelength) and the Raman scatteringwavelength λ2 are excited. The surface plasmons propagate along thesurface of the metal lattice 150 and excite the localized surfaceplasmons in the second protrusion group 205 or the third protrusiongroup 215. In addition, the localized surface plasmons excite theenhanced electric field between the protrusions 200 and 210 of thesecond protrusion group 205 or the third protrusion group 215, and thesurface-enhanced Raman scattering is generated by the interactionbetween the enhanced electric field and the target substance. In thiscase, since the interval between the protrusions 200 and 210 of thesecond protrusion group 205 or the third protrusion group 215 is narrow,a strong enhanced electric field is excited between the protrusions 200and 210. For this reason, regardless of whether the number of targetsubstances adsorbed between the protrusions 200 and 210 is singular orplural, it is possible to generate the surface-enhanced Raman scatteringby the enhanced electric field.

2.6. Incident Angle

FIGS. 19A and 19B are explanatory diagrams illustrating a technique forintroducing incident light into a sensor chip 300 with an inclination.Hereinafter, the like reference numerals denote like elements as in FIG.1B, and description thereof will not be repeated. In the example in FIG.19A, the incident light Lin is inclined with respect to the sensor chip300 by deviating an optical axis Lax1 of a light source from an opticalaxis Lax2 of an object lens 3. In the example in FIG. 19B, the opticalaxis Lax1 of the light source matches with the optical axis Lax2 of theobject lens 3, and the sensor chip 300 is inclined with respect to theoptical axis Lax2 of the object lens 3 so that the incident light Lin isinclined with respect to the sensor chip 300.

In the example in FIG. 19A, the sensor chip 300 is disposed on thesupport 430 perpendicularly to the optical axis Lax2 of the object lens3. In addition, the incident light Lin is incident to the object lens 3in parallel to the optical axis Lax of the object lens 3 by separatingthe optical axis Lax1 of the single activated light source from theoptical axis Lax2 of the object lens 3 in a predetermined distance. Thepredetermined distance is a distance at which the incident angle of theincident light Lin with respect to the sensor chip 300 becomes θ byrefraction in the object lens 3. The light Lout from the sensor chip 300is incident to the object lens 3 and guided to the half mirror 2 inFIGS. 1A to 1D by the object lens 3.

In the example in FIG. 19B, an angle between the normal line of theplane of the sensor chip 300 (the plane of the substrate 100) and theoptical axis Lax2 of the object lens 3 is set to θ. In addition, theincident light Lin from the single activated light source is incidentalong the optical axis Lax2 of the object lens 3. Then, the incidentlight Lin is incident to the sensor chip 300 with an incident angle θwithout being refracted by the object lens 3. In order to incline thesensor chip 300, as shown in FIG. 19B, the support 430 may be inclined.In addition, the support surface of the support 430 may be inclined bymodifying the example in FIG. 19B.

2.7. Optical Device (Metal Nano-structure Using Deposition)

FIGS. 20A and 20B are schematic explanatory diagrams illustrating amethod of manufacturing an electrical conductor. For example, a methodof manufacturing a metal nano-structure using a photolithographictechnique as shown in FIG. 8A is called a top-down technique, in whichthe metal nano-structure has a regular arrangement structure and alsohas a gap where an enhanced electric field is generated. In contrast,the metal nano-structure having an independent island shape formedthrough deposition has an irregular size or shape, and a gap where theenhanced electric field is generated is also irregular. That is, thereis a place where the enhanced electric field is strong and a place wherethe enhanced electric field is weak, and a polarization direction of theincident light Lin also has freedom. However, since the metalnano-structure formed through deposition has a condition that a strongenhanced electric field is generated in some places, variations in themanufacturing can be advantageously absorbed.

For example, it is possible to manufacture a metal nano-structurethrough deposition using a vacuum deposition machine. As an exemplarydeposition condition, borosilicate may be employed in the substrate 100.In addition, silver (Ag) may be employed as deposition metal, and thesilver (Ag) may be heated and deposited on the substrate 100. In thiscase, the substrate 100 is not necessary to be heated, and theheating/deposition rate may be set to 0.03 to 0.05 nm/sec.

FIG. 20A schematically illustrates a process of forming an island. Atthe initial stage of the deposition island, a seed of silver (Ag) isformed on the substrate 100. At the growth stage of the depositionisland, silver (Ag) is grown from the seed and increases in size. At thecompletion stage of the deposition island, while a distance betweenneighboring islands is reduced, the vacuum deposition may stop beforethe neighboring islands stick to each other.

In FIG. 20B, an electron microscope photograph of the metalnano-structure manufactured in practice is illustrated. In general, Agislands of approximately 25 nm are formed such that each of them isisolated. If deposition is carried out further, the Ag islands areconnected to each other, and finally, form a film. Typically, it isnecessary to deposit the islands in a regular film shape. However, inthis case, it is preferable that the independent Ag islands be narrowlyformed with a high density as long as possible.

As the plane-polarized light is irradiated onto such a metalnano-structure, a strong enhanced electric field is formed in thevicinity of the gap between the deposition islands while the position orthe direction of the gap is not constant. The thing contributing to theenhanced electric field is a P-polarized wave of the incident light Linmatching with the direction of the gap. A strong enhanced electric fieldmay be formed by the polarization direction, or a slightly weak enhancedelectric field may be formed.

2.8. Spectroscopic Analysis

FIGS. 21A to 21C are schematic explanatory diagrams illustrating peakextraction of the Raman spectrum. FIG. 21A illustrates a Raman spectrumdetected when excitation laser is irradiated onto a certain substance,in which the Raman shift is expressed using a wave number. In theexample in FIG. 21A, it is recognized that a first peak (883 cm⁻¹) and asecond peak (1453 cm⁻¹) are characteristic. By checking the obtainedRaman spectrum against the data stored in advance (for example, checkingthe light intensity and the Raman shift of the first peak, and againstthe light intensity and the Raman shift of the second peak), it ispossible to specify the target substance.

FIG. 21B illustrates a signal intensity (white circle) when a spectrumaround the second peak is detected by the optical receiver element 380using a spectroscopic element 370 having a low resolution (40 cm⁻¹).FIG. 21C illustrates a signal intensity (white circle) when a spectrumaround the second peak is detected by the optical receiver element 380using a spectroscopic element 370 having a high resolution (10 cm⁻¹).When the resolution is high such as 10 cm⁻¹, it becomes easy toaccurately specify the Raman shift (black circle) of the second peak.

While the embodiments of the invention have been described in detail inthe foregoing description, it will be appreciated by those skilled inthe art that various modifications can be made without substantiallydeparting from the novel matter and effects of the invention. Therefore,such various modifications are intended to be included in the scope ofthe invention. For example, through the description and the drawings,the terminologies referred to at least once together with other wordswhich may be broader or have the same meaning may be substituted forother terms in any parts of the description or the drawings. Inaddition, configurations or operations of the optical device, thedetection apparatus and the analysis apparatus may be variously modifiedwithout limitation to the embodiments of the invention.

The entire disclosure of Japanese Patent Application No. 2010-205510,filed Sep. 14, 2010 is expressly incorporated by reference herein.

What is claimed is:
 1. An optical device unit detachable from adetection apparatus, the optical device unit comprising: an opticaldevice having an electrical conductor, the optical device being capableof enhancing Raman scattering light generated by receiving light from alight source of the detection apparatus; and a first guide unit thatguides a gaseous sample to the optical device, wherein the first guideunit has a first fluid path through which the gaseous sample flows froman import opening of the first fluid path to the optical device, thefirst fluid path is acutely bent one or more times, and the first fluidpath has an inner surface that blocks an incident ray of external lightand that has a light reflecting property.
 2. The optical device unitaccording to claim 1, further comprising a filter for removing dust frominside the first fluid path, wherein the filter blocks the externallight.
 3. The optical device unit according to claim 1, furthercomprising an identification code that can be read by the detectionapparatus and identifies the optical device.
 4. The optical device unitaccording to claim 1, wherein the first guide unit has a second fluidpath connected to the first fluid path, and the second fluid pathrotates the gaseous sample in an area facing the optical device.
 5. Adetection apparatus comprising: the optical device unit according toclaim 1; a second guide unit connectable to the first guide unit; thelight source; a first optical system that enters the light from thelight source into the electrical conductor of the optical device; and adetector that detects Raman scattering light from the light scattered orreflected by the electrical conductor, wherein the second guide unitguides the gaseous sample to an outlet.
 6. The detection apparatusaccording to claim 5, wherein the electrical conductor of the opticaldevice includes a first protrusion group having a plurality ofprotrusions, each of the plurality of protrusions of the firstprotrusion group is arranged with a first period along a directionparallel to a conductor imaginary plane of the electrical conductor, andthe first optical system introduces the light from the light source intothe first protrusion group such that a component parallel to apolarization imaginary plane of a polarization direction of the lightfrom the light source is parallel to an arrangement direction of thefirst protrusion group.
 7. The detection apparatus according to claim 6,wherein each of the plurality of the protrusions of the first protrusiongroup includes a second protrusion group formed of an electricalconductor on a front surface of the first protrusion group, and each ofa plurality of protrusions of the second protrusion group correspondingto any one of the plurality of protrusions of the first protrusion groupis arranged with a second period shorter than the first period along adirection parallel to the virtual plane.
 8. The detection apparatusaccording to claim 6, further comprising a third protrusion group formedof a third electrical conductor on a surface between neighboringprotrusions of the first protrusion group on a surface where the firstprotrusion group is arranged, wherein each of a plurality of protrusionsof the third protrusion group is arranged with a third period shorterthan the first period along the direction parallel to the virtual planebetween the neighboring protrusions of the first protrusion group. 9.The detection apparatus according to claim 6, wherein surface plasmonresonance in the event that a propagating direction of the light fromthe light source is inclined with respect to a normal line directed tothe virtual plane is generated in each of first and second resonancepeak wavelengths, a first resonance peak wavelength band having thefirst resonance peak wavelength has an excitation wavelength insurface-enhanced Raman scattering caused by the surface plasmonresonance, and a second resonance peak wavelength band having the secondresonance peak wavelength has a Raman scattering wavelength in thesurface-enhanced Raman scattering.
 10. The detection apparatus accordingto claim 5, further comprising a second optical system that guides theRaman scattering light to the detector, wherein the detector receivesthe Raman scattering light through the second optical system.